The present invention relates to a cap with valve, such as a fuel cap for automobiles, which is installed to an aperture of a container such as a filler neck of a fuel tank and can adjust pressure in the container such as fuel tank.
Such cap is disclosed, for example, in a fuel cap for automobiles shown in FIG. 1 (refer to U.S. Pat. No. 4,337,873).
The fuel cap 1 comprises a cap body 2 threadedly engaged with a filler neck of a fuel tank, and a flowing hole 3a of round shape formed on a ceiling plate 3 of the cap body 2 so that the air can flow into the fuel tank. A valve body 8 is urged by a coil spring 6 and inserted in the flowing hole 3a from lower side so that the valve body 8 acts while pressure within the fuel tank is negative and the flowing hole 3a is closed always except the acting state.
The valve body 8 is provided at lower side with a base portion 8b to be fitted to the top end of the coil spring 6 and with a seal lip 8a in umbrella-like shape. The seal lip 8a is pressed against periphery at the bottom end of the flowing hole 3a at rear side in the inserting direction so as to close the flowing hole 3a. The valve body 8 moves downward against the biasing force of the coil spring 6 while pressure within the fuel tank is negative thereby the seal lip 8a is separated from periphery at the bottom end of the flowing hole 3a and the air flows from the flowing hole 3a into the fuel tank. Numeral 8c designates a rod portion projecting at the center of the top end of the valve body 8. The rod portion 8c is inserted in a guide hole 5a of a guide member 5 projecting on the ceiling plate 3 thereby eccentricity of the valve body 8 is prevented. Numeral 4 designates a locking lug projecting from the ceiling plate 3, and numeral 7 designates a spring shoe.
In the fuel cap 1 of the prior art, however, except the acting state of the valve 8, the seal lip 8a opened in umbrella-like shape is inserted in the flowing hole 3a and pressed against periphery at the bottom end of the flowing hole 3a so as to close the flowing hole 3a. That is, when the temperature rise is accompanied with evaporation of the fuel and the pressure within the fuel tank becomes positive pressure beyond prescribed valve, the valve body 8 is slightly moved in the inserting direction being the closing direction and is further inserted in the flowing hole 3a so that the seal lip 8a is closed.
Consequently, if the positive pressure state continues for a long period, the seal lip 8a in itself will be be closed and subjected to the premanent deformation in the closed state thereby the seal property and the negative pressure eliminating capacity of the valve body 8 may be deteriorated.